1. Field of the Invention
The present invention relates to a controller for an air conditioner, and more particularly, to a controller for an air conditioner which has a compressor of a constant speed drive type.
2. Description of the Related Art
Among air conditioners for effecting air-conditioning of an interior of a room, what is called a constant-speed type circulates refrigerant while driving a compressor to rotate at a constant rotational frequency. Further, one type of air conditioner is called a separate type, which is divided into an interior unit installed inside the room and an exterior unit installed outside the room.
In the constant-speed separate type air conditioner, a compressor is controlled in such a manner that it is turned on or off in accordance with necessity. In other words, the compressor is run or stopped when a microcomputer provided in the interior unit turns a power relay for supplying electric power to the compressor on or off, thereby controlling the compression of the refrigerant and the circulation of the refrigerant in a refrigerating cycle.
However, in such an air conditioner, if a cross flow fan is run at the start of a heating, cold air is blown out in the interior of the room because the temperature of a heat exchanger in the interior unit is as low as the room temperature. In order to prevent cold air from being blown out at the start of the heating like this, the temperature of the heat exchanger in the interior unit is measured, and after the temperature of the heat exchanger has risen to a certain degree (for example, approximately 25.degree. C.), the cross flow fan is rotated firstly at low speed so as to gently blow out air. Subsequently, when the temperature of the heat exchanger of the interior unit has risen sufficiently and exceeds a predetermined temperature (for example, approximately 35.degree. C.), the process proceeds to the heating with a set amount of air.
In this way, the air conditioner controls the amount of air to be blown out in accordance with the rise of the temperature of the heat exchanger during the heating. Then, after the temperature of the heat exchanger has exceeded the predetermined temperature, the air conditioner continues the heating while always blowing out a set amount of the heated air.
On the other hand, in the exterior unit, a protection running that forces the compressor to stop is effected when the compressor is overloaded or the outside air temperature goes down regardless of a power-on/off state of the power relay of the interior unit.
However, constant-speed type air conditioners usually do not have circuits which can detect in the interior unit a protective running of the exterior unit. For this reason, the cross flow fan continues to rotate with a set amount of air even when the compressor has stopped running. Thus, for example, during the heating, the temperature of the heat exchanger goes down gradually, thereby casing a problem that cold air or air that is felt to be cold is blown out into the interior of the room.
In the meantime, in the exterior unit, the protection running that forces the compressor to stop is effected. The forced stop of the compressor is effected not only when the compressor motor is overloaded, but also when the outside air temperature goes down during the heating as it becomes impossible to demonstrate a sufficient heating capability. This type of forced stop of the compressor interrupts the supply of the electric power to the compressor motor regardless of an on/off signal of the power relay from the microcomputer of the interior unit.
However, particularly among constant-speed type air conditioners, there are some air conditioners that eliminate as many functions as possible in order to reduce the price of the product. Further, some of them even simplify the connection between the interior unit and the exterior unit and eliminate a signal conductor for feeding the running conditions of the exterior unit back to the interior unit. In that case, the forced stop of the compressor in the exterior unit cannot be detected easily on the interior unit side. For this reason, for example, during the heating, the cross flow fan of the interior unit is kept running although the compressor of the exterior unit has been stopped by the protection running, thereby raising problems such as cold air being blown out from the interior unit.